Fuel cell system

ABSTRACT

A fuel cell system includes first and second fuel cell stacks which are juxtaposed to each other. An assembly manifold is attached to the first and second fuel cell stacks. A connection block is provided at a central position of the assembly manifold. A fuel gas supply port and a fuel gas discharge port are provided on a front surface of the connection block, and an oxygen-containing gas supply port and an oxygen-containing gas discharge port are provided on a back surface of the connection block. A fuel gas and an oxygen-containing gas are equally supplied to each of the first and second fuel cell stacks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell system including a fuelcell stack formed by stacking a plurality of unit cells in a horizontaldirection. Each of the unit cells includes an electrolyte electrodeassembly and separators sandwiching the electrolyte electrode assembly.The electrolyte electrode assembly includes a pair of electrodes and anelectrolyte interposed between the electrodes. Six fluid passages extendthrough the unit cells in the stacking direction. Three of the six fluidpassages are provided on the left of the unit cells, and the other threeof the six fluid passages are provided on the right of the unit cells.

2. Description of the Related Art

For example, a solid polymer fuel cell employs a membrane electrodeassembly which includes an anode and a cathode, and an electrolytemembrane (electrolyte) interposed between the anode and the cathode. Theelectrolyte membrane is a polymer ion exchange membrane. Each of theanode and the cathode is made of electrode catalyst layer of noble metalformed on a base material chiefly containing carbon. The membraneelectrode assembly and separators sandwiching the membrane electrodeassembly make up a unit of a fuel cell for generating electricity.

In the fuel cell, a fuel gas such as a gas chiefly containing hydrogen(hereinafter also referred to as the hydrogen-containing gas) issupplied to the anode. The catalyst of the anode induces a chemicalreaction of the fuel gas to split the hydrogen molecule into hydrogenions and electrons. The hydrogen ions move toward the cathode throughthe electrolyte, and the electrons flow through an external circuit tothe cathode, creating a DC electric current. A gas chiefly containingoxygen or air (hereinafter also referred to as the oxygen-containinggas) is supplied to the cathode. At the cathode, the hydrogen ions fromthe anode combine with the electrons and oxygen to produce water.

Generally, a predetermined number of, e.g., several tens to severalhundreds of fuel cells are stacked together to form a fuel cell stackfor achieving the desired level of electricity in power generation. Thefuel cell is considerably long in the stacking direction. Therefore, itis not possible to supply the fuel gas equally to each of the fuelcells. In order to address the problem, a fuel cell system including aplurality of juxtaposed fuel cell stacks has been proposed. For example,International Patent Publication No. 96/20509 titled “INTEGRATEDEXTERNAL MANIFOLD ASSEMBLY FOR AN ELECTROCHEMICAL FUEL CELL STACK ARRAY”is known. In the conventional technique, as shown in FIG. 9, anelectrochemical fuel cell stack array 1 includes four fuel cell stacks 2a through 2 d. Each of the fuel cell stacks 2 a through 2 d is formed bystacking a plurality of unit cells 3 in a stacking direction indicatedby an arrow X.

The electrochemical fuel cell stack array 1 is connected to externalmanifold assemblies 4. The external manifold assemblies 4 include asupply manifold comprising main pipes 5 a, 5 b, 5 c, and a dischargemanifold comprising main pipes 6 a, 6 b, 6 c.

The fuel gas, the oxygen-containing gas, and the coolant flow throughthe main pipes 5 a through 5 c. For example, a plurality of manifoldbifurcated pipes 7 for supplying the reactant gases to each of the fuelcell stacks 2 a through 2 d are connected to the manifold main pipe 5 a.

Likewise, the fuel gas, the oxygen-containing gas, and the coolant flowthrough the main pipes 6 a through 6 c. For example, a plurality ofmanifold bifurcated pipes 8 for discharging the reactant gases from eachof the fuel cell stacks 2 a through 2 d are connected to the manifoldmain pipe 6 a.

However, in the conventional technique, since the external manifoldassemblies 4 are provided on opposite ends of the electrochemical fuelcell stack array 1 in the direction indicated by the arrow X, theoverall size of the electrochemical fuel cell stack array 1 isconsiderably large. The piping system is complicated and large. Thus,the operation of connecting the pipes is laborious, and theelectrochemical fuel cell stack array 1 cannot be installed in a smallspace. In particular, the electrochemical fuel cell stack array 1 is notsuitable for use in a vehicle.

Further, the manifold bifurcated pipes 7 branched from the main pipe 5 aand the manifold bifurcated pipes 8 branched from the main pipe 6 a havedifferent lengths corresponding to the supply ports and discharge portsof the respective fuel cell stacks 2 a through 2 d. Therefore, it is notpossible to provide the reactant gases to each of the fuel cell stacks 2a through 2 c uniformly.

SUMMARY OF THE INVENTION

A main object of the present invention is to provide a fuel cell systemwhich makes it possible to simplify and downsize the piping structure ofa fuel cell stack effectively, reduce the number of components, andsimplify the assembling operation.

According to an aspect of the present invention, a fuel cell systemincludes first and second fuel cell stacks having the same structure.Each of the first and second fuel cell stacks is formed by stacking aplurality of unit cells in a horizontal direction. Each of the unitcells includes an electrolyte electrode assembly and separatorssandwiching the electrolyte electrode assembly. The electrolyteelectrode assembly includes a pair of electrodes and an electrolyteinterposed between the electrodes. Three of six fluid passagescomprising a fuel gas supply passage, an oxygen-containing gas supplypassage, a coolant supply passage, a fuel gas discharge passage, anoxygen-containing gas discharge passage, and a coolant discharge passageextend through a left end of each of the first and second fuel cellstacks, and the other three of the six fluid passages extend through aright end of each of the first and second fuel cell stacks. The firstand second fuel cell stacks are juxtaposed along the stacking directionsuch that polarity of the first fuel cell stack and polarity of thesecond fuel cell stack are oriented oppositely. An assembly manifold isconnected to first and second end plates provided adjacent to each otherat one end of the first and second fuel cells.

The assembly manifold includes a plurality of pipes for supplying thefuel gas, the oxygen-containing gas, and the coolant to the first andsecond fuel cell stacks and discharging the fuel gas, theoxygen-containing gas, and the coolant from the first and second fuelcell stacks, and a connection block provided at a central position ofthe assembly manifold. The connection block has at least a supply portand a discharge port of the fuel gas, and a supply port and a dischargeport of the oxygen-containing gas.

According to another aspect of the present invention, a fuel cell systemincludes a fuel cell stack formed by stacking a plurality of unit cellsin a horizontal direction. Each of the unit cells includes anelectrolyte electrode assembly and separators sandwiching theelectrolyte electrode assembly, and the electrolyte electrode assemblyincludes a pair of electrodes and an electrolyte interposed between theelectrodes. Three of six fluid passages comprising a fuel gas supplypassage, an oxygen-containing gas supply passage, a coolant supplypassage, a fuel gas discharge passage, an oxygen-containing gasdischarge passage, and a coolant discharge passage extend through a leftend of the fuel cell stack, and the other three of the six fluidpassages extend through a right end of the fuel cell stack.

A single first manifold is connected to three fluid passages provided atone end of the first fuel cell stack. A single second manifold isconnected to three fluid passages provided at the other end of the firstfuel cell stack. The first and second manifolds are connected by aplurality of pipes.

According to the present invention, since the connection block isprovided at a central position of the assembly manifold, the fuel gasand the oxygen-containing gas is equally distributed to each of thefirst and second fuel cell stacks provided on the left and right sides.Therefore, the desired power generation performance is reliablymaintained in the first and second fuel cell stacks.

Further, the assembly manifold is attached to the end plate of the firstfuel cell stack and the end plate of the second fuel cell stack whichare adjacent to each other at one end of the first and second fuel cellstacks. Therefore, the overall size of the fuel cell system is small,and the piping structure and the piping operation are simplified.

The fuel gas supply port and the fuel gas discharge port are provided onthe front surface of the connection block, and the oxygen-containing gassupply port and the oxygen-containing gas discharge port are provided onthe back surface of the connection block. Therefore, sufficient spacefor providing the pipes and joints is available on both surfaces (thefront surface and the back surface) of the connection block. Ahumidifier may be provided between the first and second fuel cell stacksto reduce the piping distance between the humidifier and the connectionblock effectively.

According to the present invention, since each of the manifolds isconnected to three fluid passages, the number of components of the fuelcell system is considerably reduced, and the overall assemblingoperation of the assembly manifold is suitably simplified.

Further, a plurality of the pipes are provided in contact with thesurface of the end-plate. The reactant gas and the oxygen-containing gasdischarged from the first fuel cell stack have high temperature, and thehot reactant gas and the hot coolant are used for heating the end plate.Therefore, with the simple structure, warming up process in the fuelcell stack is carried out rapidly.

Further, the adjacent pipes of the plurality of pipes are in contactwith each other. The coolant and the oxygen-containing gas dischargedfrom the first fuel cell stack are used for heating the coolant and theoxygen-containing gas supplied to the fuel cell stack. Therefore, thetemperature in the fuel cell stack is uniform, and the power generationis carried out efficiently.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing the overall structureof a fuel cell system according to an embodiment of the presentinvention;

FIG. 2 is a cross sectional side view showing part of a fuel cell stackof the fuel cell system;

FIG. 3 is an exploded perspective view showing a unit cell of the fuelcell stack;

FIG. 4 is a perspective view showing the fuel cell stack;

FIG. 5 is a view showing flows of reactant gases and a coolant in thefuel cell system;

FIG. 6 is a view showing flows of the reactant gases and the coolant inan assembly manifold of the fuel cell system;

FIG. 7 is a cross sectional view showing a connection block of theassembly manifold;

FIG. 8 is a front view showing the assembly manifold; and

FIG. 9 is a view showing a conventional assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view schematically showing the overall structureof a fuel cell system 10 according to an embodiment of the presentinvention.

The fuel cell system 10 includes a first fuel stack 12 and a second fuelcell stack 14 having the same structure. The first fuel cell stack 12and the second fuel cell stack 14 are juxtaposed in a horizontaldirection such that the polarity of the first fuel cell stack 12 and thepolarity of the second fuel cell stack 14 are oriented oppositely. Anassembly manifold 16 is attached to a horizontal end of the first andsecond fuel cell stacks 12, 14.

As shown in FIG. 2, the first fuel cell stack 12 includes a stack body20 formed by stacking a plurality of unit cells 18 in a horizontaldirection indicated by an arrow A. At an end of the stack body 20 in thestacking direction indicated by the arrow A, a terminal plates 22 a isprovided. An insulating plate 24 is provided outside the terminal plate22 a. Further, a first end plate 26 a is provided outside the insulatingplate 24. At the other end of the stack body 20 in the stackingdirection, a terminal plate 22 b is provided. An insulating spacermember 28 is provided outside the terminal plate 22 b. Further, a secondend plate 26 b is provided outside the insulating spacer member 28. Eachof the first and second end plates 26 a, 26 b has a rectangular shape.The first fuel cell stack 12 is assembled together such that the stackbody 20 formed by stacking the unit cells 18 is housed in a casing 29including the end plates 26 a, 26 b.

As shown in FIGS. 2 and 3, each of the unit cells 18 includes a membraneelectrode assembly (electrolyte electrode assembly) 30 and first andsecond metal separators 32, 34 sandwiching the membrane electrodeassembly 30. The first and second metal separators 32, 34 are thincorrugated plates.

At one end of the unit cell 18 in a longitudinal direction indicated byan arrow B in FIG. 3, an oxygen-containing gas supply passage 36 a forsupplying an oxygen-containing gas, a coolant supply passage 38 a forsupplying a coolant, and a fuel gas discharge passage 40 b fordischarging a fuel gas such as a hydrogen-containing gas are provided.The oxygen-containing gas supply passage 36 a, the coolant supplypassage 38 a, and the fuel gas discharge passage 40 b extend through theunit cell 18 in the direction indicated by the arrow A.

At the other end of the unit cell 18 in the longitudinal direction, afuel gas supply passage 40 a for supplying the fuel gas, a coolantdischarge passage 38 b for discharging the coolant, and anoxygen-containing gas discharge passage 36 b for discharging theoxygen-containing gas are provided. The fuel gas supply passage 40 a,the coolant discharge passage 38 b, and the oxygen-containing gasdischarge passage 36 b extend through the unit cell 18 in the directionindicated by the arrow A.

The membrane electrode assembly 30 includes an anode 44, a cathode 46,and a solid polymer electrolyte membrane 42 interposed between the anode44 and the cathode 46. The solid polymer electrolyte membrane 42 isformed by impregnating a thin membrane of perfluorosulfonic acid withwater, for example.

Each of the anode 44 and the cathode 46 has a gas diffusion layer (notshown) such as a carbon paper, and an electrode catalyst layer (notshown) of platinum alloy supported on porous carbon particles. Thecarbon particles are deposited uniformly on the surface of the gasdiffusion layer. The electrode catalyst layer of the anode 44 and theelectrode catalyst layer of the cathode 46 are fixed to both surfaces ofthe solid polymer electrolyte membrane 42, respectively.

The first metal separator 32 has a fuel gas flow field 48 on its surface32 a facing the membrane electrode assembly 30. The fuel gas flow field48 is connected to the fuel gas supply passage 40 a at one end, andconnected to the fuel gas discharge passage 40 b at the other end. Thefuel gas flow field 48 includes a plurality of grooves extending in thedirection indicated by the arrow B, for example. Further, the firstmetal separator 32 has a coolant flow field 50 on the other surface 32b. The coolant flow field 50 is connected to the coolant supply passage38 a at one end, and connected to the coolant discharge passage 38 b atthe other end. The coolant flow field 50 includes a plurality of groovesextending in the direction indicated by the arrow B.

The second metal separator 34 has an oxygen-containing gas flow field 52on its surface 34 a facing the membrane electrode assembly 30. Theoxygen-containing gas flow field 52 is connected to theoxygen-containing gas supply passage 36 a at one end, and connected tothe oxygen-containing gas discharge passage 36 b at the other end. Theoxygen-containing gas flow field 52 includes a plurality of groovesextending in the direction indicated by the arrow B. The other surface34 b of the second metal separator 34 is stacked on the surface 32 b ofthe first metal separator 32. When the first metal separator 32 and thesecond metal separator 34 are stacked together, the coolant flow field50 is formed between the surface 32 b of the first metal separator 32and the surface 34 b of the second metal separator 34.

A first seal member 54 is formed integrally on the surfaces 32 a, 32 bof the first metal separator 32 to cover (sandwich) the outer edge ofthe first metal separator 32. The first seal member 54 is providedaround the fuel gas supply passage 40 a, the fuel gas discharge passage40 b, and the fuel gas flow field 48 on the surface 32 a of the firstmetal separator 32. The first seal member 54 is not provided between thefuel gas supply passage 40 a and the fuel gas flow field 48, and betweenthe fuel gas discharge passage 40 b and the fuel gas flow field 48.Thus, the fuel gas supply passage 40 a and the fuel gas dischargepassage 40 b are connected to the fuel gas flow field 48.

A second seal member 56 is formed integrally on the surfaces 34 a, 34 bof the second metal separator 34 to cover (sandwich) the outer edge ofthe second metal separator 34. The second seal member 56 is providedaround the oxygen-containing gas supply passage 36 a, theoxygen-containing gas discharge passage 36 b, and the oxygen-containinggas flow field 52 on the surface 34 a of the second metal separator 34.The second seal member 56 is not provided between the oxygen-containinggas supply passage 36 a and the oxygen-containing gas flow field 52, andbetween the oxygen-containing gas discharge passage 36 b and theoxygen-containing gas flow field 52. Thus, the oxygen-containing gassupply passage 36 a and the oxygen-containing gas discharge passage 36 bare connected to the oxygen-containing gas flow field 52.

The first seal member 54 is provided around the coolant supply passage38 a, the coolant discharge passage 38 b, and the coolant flow field 50on the surface 32 b of the first metal separator 32. The second sealmember 56 is provided around the coolant supply passage 38 a, thecoolant discharge passage 38 b, and the coolant flow field 50 on thesurface 34 b of the second metal separator 32. The first seal member 54and the second seal member 56 are not provided between the coolantsupply passage 38 a and the coolant flow field 50, and between thecoolant discharge passage 38 b and the coolant flow field 50. Thus, thecoolant supply passage 38 a and the coolant discharge passage 38 b areconnected to the coolant gas flow field 50.

As shown in FIG. 2, a seal 57 is interposed between the first and secondseal members 54, 56 so that the outer edge of the solid polymerelectrolyte membrane 42 does not directly contact the casing 29. A smallclearance may be formed between the outer edges of the first and secondseal members 54, 56, and an inner surface of the casing 29.Alternatively, the outer edges of the first and second seal members 54,56 may be in contact with the inner surface of the casing 29. In thestructure, the first and second metal separators 32, 34 are not deformedexcessively beyond a predetermined extent. As shown in FIGS. 1 and 2,plate-shaped terminals 58 a, 58 b extend from the terminal plates 22 a,22 b along a surface of the fuel cell stack 12, respectively.

As shown in FIGS. 2 and 4, the casing 29 includes the end plates 26 a,26 b, a plurality of side plates 60 a to 60 d, angle members (e.g., Langles) 62 a to 62 d, and coupling pins 64 a, 64 b. The side plates 60 ato 60 d are provided on sides of the stack body 20. The angle members 62a to 62 d are used as coupling members for coupling adjacent ends of theside plates 60 a to 60 d. The coupling pins 64 a, 64 b are used forcoupling the end plates 26 a, 26 b and the side plates 60 a to 60 d. Thelength of the coupling pins 64 a is short in comparison with the lengthof the coupling pins 64 b.

As shown in FIG. 4, at one end of the first end plate 26 a in thedirection indicated by an arrow B, an oxygen-containing gas inlet port66 a connected to the oxygen-containing gas supply passage 36 a, acoolant inlet port 68 a connected to the coolant supply passage 38 a,and a fuel gas outlet port 70 b connected to the fuel gas dischargepassage 40 b are provided.

At the other end of the first end plate 26 a in the direction indicatedby the arrow B, a fuel gas inlet port 70 a connected to the fuel gassupply passage 40 a, a coolant outlet port 68 b connected to the coolantdischarge passage 38 b, and an oxygen containing gas outlet port 66 bconnected to the oxygen-containing gas discharge passage 36 b areprovided.

As shown in FIG. 2, the spacer member 28 has a rectangular shape havingpredetermined dimensions such that the spacer member 28 is positionedinside the casing 29. The thickness of the spacer member 28 is selectedsuch that the dimensional variation in the stacking direction of thestack body 20 is absorbed, and the desired tightening force is appliedto the stack body 20. However, the use of the spacer member 28 is notessential to carry out the present invention. The spacer member 28 maynot be used in the case where the dimensional variation in the stackingdirection is absorbed by the elasticity of the first and second metalseparators 32, 34, for example.

The structure of the second fuel cell stack 14 is substantially the sameas the above-described structure of the first fuel cell stack 12. Theconstituent elements of the second fuel cell stack 14 that are identicalto those of the first fuel cell stack 12 are labeled with the samereference numeral, and description thereof will be omitted.

The stack body 20 of the first fuel cell stack 12 and the stack body 20of the second fuel cell stack 14 have totally the same structure. Thepolarity of the first fuel cell stack 12 is opposite to the polarity ofthe second fuel cell stack 14. For example, the stack body 20 of thesecond fuel cell stack 14 is symmetrical about a point with respect tothe stack body 20 of the first fuel cell stack 12. The position of thestack body 20 of the second fuel cell stack 14 is reversed by 180° abouta vertical axis from the position of the stack body 20 of the first fuelcell stack 12.

As shown in FIG. 5, in the second fuel cell stack 14, the second endplate 26 b has an oxygen-containing gas inlet port 72 a, a coolant inletport 74 a, and a fuel gas outlet port 76 b at one end in the directionindicated by the arrow B, and has a fuel gas inlet port 76 a, a coolantoutlet port 74 b, and an oxygen-containing outlet port 72 b at the otherend in the direction indicated by the arrow B.

The oxygen-containing gas inlet ports 66 a, 72 a, the coolant inletports 68 a, 74 a, the fuel gas outlet ports 70 b, 76 b, the fuel gasinlet ports 70 a, 76 a, the coolant outlet ports 68 b, 74 b, and theoxygen-containing gas outlet ports 66 b, 72 b are provided symmetricallywith respect to each other about an intermediate position P between thefirst fuel cell stack 12 and the second fuel cell stack 14. Theoxygen-containing gas inlet ports 66 a, 72 a are positioned adjacent toeach other, the coolant inlet ports 68 a, 74 a are positioned adjacentto each other, and the fuel gas outlet ports 70 b, 76 b are positionedadjacent to each other. The fuel gas inlet ports 70 a, 76 a arepositioned remote from each other, the coolant outlet ports 68 b, 74 aare positioned remote from each other, and the oxygen-containing gasoutlet ports 66 b, 72 b are positioned remote from each other.

As shown in FIG. 1, the assembly manifold 16 is attached to the firstand second end plates 26 a, 26 b which are positioned adjacent to eachother at one end of the first and second fuel cell stacks 12, 14. Asshown in FIGS. 1 and 6, a connection block 80 is provided at a centralposition of the assembly manifold 16. Six pipes 82 a through 82 f areconnected to one side of the connection block 80, and six pipes 84 athrough 84 f are connected to the other side of the connection block 80.

The pipes 82 a through 82 f extend toward the side of the first fuelcell stack 12, and are connected to a first manifold 86. The firstmanifold 86 is an single manifold connected to the oxygen-containing gasinlet port 66 a, the coolant inlet port 68 a, and the fuel gas outletport 70 b as holes of three fluid passages formed at one end (left end)of the first fuel cell stack 12.

The fuel gas inlet port 70 a, the coolant outlet port 68 b, and theoxygen-containing gas outlet port 66 b as holes of three fluid passagesformed at the other end (right end) of the first fuel cell stack 12 areconnected to a single second manifold 88. The first manifold 86 isconnected to ends of the four pipes 90 a through 90 d. The pipes 90 athrough 90 d are in fluid communication with the pipes 82 b through 82e, respectively.

The other ends of the pipes 90 a, 90 b, and 90 d are connected to thesecond manifold 88. The other end of the pipe 90 c extends around thesecond manifold 88, along the side of the first fuel cell stack 12. Theouter circumferential surfaces of the pipes 90 a through 90 d are incontact with each other, and in contact with the surface of the firstend plate 26 a of the first fuel cell stack 12.

The pipes 84 a through 84 f extend toward the second fuel cell stack 14,and are connected to a third manifold 92.

The third manifold 92 is an single manifold connected to theoxygen-containing gas inlet port 72 a, the coolant inlet port 74 a, andthe fuel gas outlet port 76 b as holes of three fluid passages formed atone end (right end) of the second fuel cell stack 14.

The fuel gas inlet port 76 a, the coolant outlet port 74 b, and theoxygen-containing gas outlet port 72 b as holes of three fluid passagesformed at the other end (left end) of the second fuel cell stack 14 areconnected to a single fourth manifold 94.

The third manifold 92 is connected to ends of the four pipes 96 athrough 96 d. The pipes 96 a through 96 d are in fluid communicationwith the pipes 84 b through 84 e, respectively. The other ends of thepipes 96 a, 96 c, and 96 d are connected to the fourth manifold 94. Theother end of the pipe 96 b is partially connected to the fourth manifold94, and extends along the side of the second fuel cell stack 14.

A fuel gas supply port 98 a and a fuel gas discharge port 98 b areformed on one surface (front surface) 80 a of the connection block 80.The fuel gas supply port 98 a is connected to the pipes 82 b, 84 b, andthe fuel gas discharge port 98 b is connected to the pipes 82 f, 84 f.

As shown in FIG. 7, an oxygen-containing gas supply port 100 a and anoxygen-containing gas discharge port 100 b are formed adjacent to eachother at an upper position of the opposite surface (back surface) 80 bof the connection block 80. The oxygen-containing gas supply port 100 ais connected to the pipes 82 a, 84 b, and the oxygen-containing gasdischarge port 100 b is connected to the pipes 82 e, 84 e. A humidifier102 is attached to the back surface 80 b. The humidifier 102 isconnected to the oxygen-containing gas supply port 100 a and theoxygen-containing gas discharge port 10 b.

As shown in FIGS. 6 and 8, in the first manifold 86, theoxygen-containing gas inlet port 66 a is connected to the pipe 82 a, thecoolant inlet port 68 b is connected to the pipes 82 d, 90 c, and thefuel gas outlet port 70 b is connected to the pipe 82 f. In the secondmanifold 88, the fuel gas inlet port 70 a is connected to the pipe 90 a,the coolant inlet port 68 b is connected to the pipe 90 b, and theoxygen-containing gas outlet port 66 b is connected to the pipe 90 d.

Likewise, in the third manifold 92, the oxygen-containing gas inlet port72 a is connected to the pipe 84 a, the coolant inlet port 74 a isconnected to the pipe 84 d, and the fuel gas discharge port 76 b isconnected to the pipe 84 f. The coolant inlet port 74 a is connected tothe pipe 96 c as necessary. The pipe 96 c has a closed end. In thefourth manifold 94, the fuel gas inlet port 76 a is connected to thepipe 96 a, the coolant outlet port 74 b is connected to the pipe 96 b,and the oxygen-containing gas outlet port 72 b is connected to the pipe96 d.

In the assembly manifold 16, the pipes 82 a, 84 a function as supplypipes for the oxygen-containing gas, the pipes 82 b, 84 b, 90 a, and 96a function as supply pipes for the fuel gas, the pipes 82 c, 84 c, 90 b,96 b function as discharge pipes for the coolant, the pipes 82 d, 84 d,90 c function as the supply pipes for the coolant, the pipes 82 e, 84 e,90 d, 96 d function as discharge pipes for the oxygen-containing gas,and the pipes 82 f, 84 f function as discharge pipes for the fuel gas.

For example, the pipes 82 a through 82 f, 84 a through 84 f, 90 athrough 90 d, and 96 a through 96 d are made of metal material havinghigh thermal conductivity, thermally conductive resin material, orinsulating resin material or the like. Insulating coating may be appliedto the flow field made of metal material.

As shown in FIG. 1, the terminal 58 a of the first fuel cell stack 12adjacent to the assembly manifold 16 and the terminal 58 b of the secondfuel cell stack 14 adjacent to the assembly manifold 16 are connectedelectrically by a cable 104. For example, the terminal 58 a has negativepolarity, and the terminal 58 b has positive polarity. The terminal 58 aand the terminal 58 b are connected electrically by the cable 104 forconnecting the first and second fuel cell stacks 12, 14 serially. Theterminal 58 b of the first fuel cell stack 12 and the terminal 58 a ofthe second fuel cell stack 14 are connected to an external load 106 suchas a motor.

Next, operation of the fuel cell system 10 will be described below.

Firstly, as shown in FIGS. 1, 6 and 7, an oxygen-containing gas issupplied from the humidifier 102 attached to the assembly manifold 16 tothe oxygen-containing gas supply port 100 a of the connection block 80,and a fuel gas such as a hydrogen-containing gas is supplied to the fuelgas supply port 98 a of the connection block 80. Further, a coolant suchas pure water, an ethylene glycol or an oil is supplied to the pipe 90c.

The oxygen-containing gas supplied to the oxygen-containing gas supplyport 100 a of the connection block 80 flows through the pipes 82 a, 84 ato the first and third manifolds 86, 92. Thus, the oxygen-containing gasis supplied to the oxygen-containing gas inlet ports 66 a, 72 a of thefirst and second end plates 26 a, 26 b of the first and second fuel cellstacks 12, 14 (see FIGS. 5 and 6).

The fuel gas supplied to the fuel gas supply port 98 a of the connectionblock 80 flows through the pipes 82 b, 84 b, and the pipes 90 a, 96 a tothe fuel gas inlet ports 70 a, 76 a of the first and second fuel cellstacks 12, 14.

Some of the coolant supplied to the pipe 90 c flows from the secondmanifold 88 to the coolant inlet port 68 a of the first fuel cell stack12, and the remaining coolant flows through the pipes 82 d, 84 d, andare supplied from the third manifold 92 to the coolant inlet port 74 aof the second fuel cell stack 14.

Then, in the first fuel cell stack 12, as shown in FIG. 3, theoxygen-containing gas flows from the oxygen-containing gas supplypassage 36 a into the oxygen-containing gas flow field 52 of the secondmetal separator 34. The oxygen-containing gas flows along the cathode 46of the membrane electrode assembly 30 for inducing an electrochemicalreaction at the cathode 46. The fuel gas flows from the fuel gas supplypassage 40 a into the fuel gas flow field 48 of the first metalseparator 32 for inducing an electrochemical reaction at the anode 44.

Thus, in each of the membrane electrode assemblies 30, theoxygen-containing gas supplied to the cathode 46, and the fuel gassupplied to the anode 44 are consumed in the electrochemical reactionsat catalyst layers of the cathode 46 and the anode 44 for generatingelectricity.

After the oxygen in the oxygen-containing gas is consumed at the cathode46, the oxygen-containing gas flows into the oxygen-containing gasdischarge passage 36 b, and is discharged from the oxygen-containing gasoutlet port 66 b of the first end plate 26 a (see FIG. 5). Likewise,after the fuel gas is consumed at the anode 44, the fuel gas flows intothe fuel gas discharge passage 40 b, and is discharged from the fuel gasoutlet port 70 b of the first end plate 26 a.

The coolant flows from the coolant flow passage 38 a into the coolantflow field 50 between the first and second metal separators 32, 34, andflows in the direction indicated by the arrow B. After the coolant isused for cooling the membrane electrode assembly 30, the coolant flowsinto the coolant discharge passage 38 b, and is discharged from thecoolant outlet port 68 b of the first end plate 26 a.

In the second fuel cell stack 14, in the same manner as the case of thefirst fuel cell stack 12, the consumed oxygen-containing gas isdischarged from the oxygen-containing gas outlet port 72 b of the secondend plate 26 b (see FIG. 5). Further, the consumed fuel gas isdischarged from the fuel gas outlet port 76 b of the second end plate 26b. After the coolant is used for cooling the membrane electrode assembly30, the coolant is discharged from the coolant outlet port 74 b of thesecond end plate 26 b.

As shown in FIGS. 6 and 8, the oxygen-containing gas discharged from theoxygen-containing gas outlet ports 66 b, 72 b flows from the second andfourth manifolds 88, 94 to the pipes 90 d, 96 d, and the pipes 82 e, 84e. Further, the oxygen-containing gas moves upwardly in the connectionblock 80, and flows from the oxygen-containing gas discharge port 100 bto the humidifier 102 (see FIG. 7).

At the humidifier 102, heat and moisture are exchanged between theoxygen-containing gas before consumption and the oxygen-containing gasafter consumption. Therefore, the oxygen-containing gas beforeconsumption is adjusted at the desired humidity and the desiredtemperature, and then, supplied to the first and second fuel cell stacks12, 14.

As shown in FIGS. 6 and 8, the fuel gas discharged from the fuel gasoutlet ports 70 b, 76 d flows from the first and third manifolds 86, 92through the pipes 82 f, 84 f to the fuel gas discharge port 98 b of theconnection block 80.

Further, the coolant discharged from the coolant discharge port 68 bflows from the second manifold 88 through the pipe 90 b to the firstmanifold 86. Then, the coolant flows through the pipes 82 c, 84 c, 96 band is discharged to the outside. Further, the coolant discharged fromthe coolant outlet port 74 b is joined in the middle of the pipe 96 b,and then, the coolant is discharged to the outside.

In the embodiment of the present invention, the first and second fuelcell stacks 12, 14 are juxtaposed, and the assembly manifold 16 isattached to the adjacent first and second end plates 26 a, 26 b of thefirst and second fuel cell stacks 12, 14. The connection block 80 isprovided at the central position of the assembly manifold 16. Theconnection block 80 has the fuel gas supply port 98 a, the fuel gasdischarge port 98 b, the oxygen-containing gas supply port 100 a, andthe oxygen-containing gas discharge port 100 b.

Thus, the fuel gas and the oxygen-containing gas are equally distributedfrom the connection block 80 to each of the first and second fuel cellstacks 12, 14. The desired power generation performance is maintained inthe first and second fuel cell stacks 12, 14.

Further, the assembly manifold 16 is attached to the adjacent first andsecond end plates 26 a, 26 b at one end of the first fuel cell stack 12and the second fuel cell stack 14. Therefore, the overall size of thefuel cell system 10 is small, and the piping structure and the pipingoperation are simplified.

The fuel gas supply port 98 a and the fuel gas discharge port 98 b areprovided on the front surface 80 a of the connection block 80, and theoxygen-containing gas supply port 100 a and the oxygen-containing gasdischarge port 100 b are provided on the back surface 80 b of theconnection block 80 (see FIG. 7). Therefore, sufficient space forproviding the pipes and joints is available on both surfaces (the frontsurface 80 a and the back surface 80 b) of the connection block 80.Thus, the space in the fuel cell system 10 is used efficiently.

The humidifier 102 is provided between the first and second fuel cellstacks 12, 14. Therefore, the piping distance between the humidifier 102and the connection block 80 is reduced effectively.

In the embodiment of the present invention, as shown in FIG. 6, thefirst fuel cell stack 12 has the single first manifold 86 connected tothe oxygen-containing gas inlet port 66 a, the coolant inlet port 68 a,and the fuel gas outlet port 70 b, and the single second manifold 88connected to the fuel gas inlet port 70 a, the coolant outlet port 68 b,and the oxygen-containing gas outlet port 66 b. Likewise, the secondfuel cell stack 14 has the single third manifold 92 connected to thethree fluid passages and the single fourth manifold 94 connected to thethree fluid passages. Therefore, the number of components of the fuelcell system 10 is considerably reduced, and the overall assemblingoperation of the assembly manifold 16 is suitably simplified.

Further, in the first fuel cell stack 12, a plurality of the pipes 90 athrough 90 d are provided in contact with the surface of the first endplate 26 a. The coolant and the oxygen-containing gas discharged fromthe first fuel cell stack 12 have high temperature due to powergeneration in the first fuel cell stack 12. When the coolant and theoxygen-containing gas flow through the pipes 90 b, 90 d, the heat istransferred from the pipes 90 b, 90 d to the first end plate 26 a.

Therefore, in particular, when operation of the first fuel cell stack 12is started at a low temperature, it is possible to rapidly warm up theend cell (unit cell provided at the end in the stacking direction) ofthe first fuel cell stack 12. With the simple structure, it is possibleto warm up the first fuel cell stack 12 efficiently.

Further, the adjacent pipes of the pipes 90 a through 90 d are incontact with each other. The coolant and the oxygen-containing gasdischarged from the first fuel cell stack 12 have high temperature. Thehot coolant and the oxygen-containing gas flowing through the pipes 90b, 90 d are used for heating the coolant and the oxygen-containing gasflowing through the pipes 90 a, 90 c toward the first fuel cell stack12.

Therefore, the temperature in the first fuel cell stack 12 is uniform,and the power generation is carried out efficiently. In the second fuelcell stack 14, the same advantages as with the first fuel cell stack 12can be obtained.

In the embodiment of the present invention, the angle members 62 a to 62d are used as the coupling members for example. However, it is notessential to use the angle members 62 a to 62 d. For example, the sideplates 60 a to 60 d may have flanges which can be bent such that theflanges can be fixed by screws to couple the side plates 60 a to 60 dwith each other. Alternatively, the side plates 60 a to 60 d may becombined together by welding to function as the coupling members.

While the invention has been particularly shown and described withreference to preferred embodiments, it will be understood thatvariations and modifications can be effected thereto by those skilled inthe art without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A fuel cell system comprising first and second fuel cell stackshaving the same structure, wherein each of said first and second fuelcell stacks is formed by stacking a plurality of unit cells in ahorizontal direction; each of said unit cells includes an electrolyteelectrode assembly and separators sandwiching said electrolyte electrodeassembly, and said electrolyte electrode assembly comprises a pair ofelectrodes and an electrolyte interposed between said electrodes; threeof six fluid passages comprising a fuel gas supply passage, anoxygen-containing gas supply passage, a coolant supply passage, a fuelgas discharge passage, an oxygen-containing gas discharge passage, and acoolant discharge passage extend through a left end of each of saidfirst and second fuel cell stacks, and the other three of the six fluidpassages extend through a right end of each of said first and secondfuel cell stacks; and an assembly manifold is connected to first andsecond end plates provided adjacent to each other at one end of saidfirst and second fuel cell stacks, said assembly manifold comprising: aplurality of pipes for supplying the fuel gas, the oxygen-containinggas, and the coolant to said first and second fuel cell stacks anddischarging the fuel gas, the oxygen-containing gas, and the coolantfrom said first and second fuel cell stacks; and a connection blockprovided at a central position of said assembly manifold, saidconnection block having at least a supply port and a discharge port ofthe fuel gas, and a supply port and a discharge port of theoxygen-containing gas.
 2. A fuel cell system according to claim 1,wherein said supply port and said discharge port of the fuel gas areprovided on one surface of said connection block, and said supply portand said discharge port of the oxygen-containing gas are provided on theopposite surface of said connection block.
 3. A fuel cell systemaccording to claim 1, wherein said assembly manifold comprises: a-singlefirst manifold connected to three fluid passages extending through saidleft end of said first fuel cell stack; a single second manifoldconnected to three fluid passages extending through said right end ofsaid first fuel cell stack; a single third manifold connected to threefluid passages extending through said right end of said second fuel cellstack; and a-single fourth manifold connected to three passagesextending through said left end of said second fuel cell stack.
 4. Afuel cell system according to-claim 1, wherein said plurality of pipesare in contact with said first and second end plates.
 5. A fuel cellsystem according to claim 1, wherein adjacent pipes of said plurality ofpipes are in contact with each other.
 6. A fuel cell system according toclaim 1, wherein a humidifier is provided between said first and secondfuel cell stacks, and said humidifier uses the oxygen-containing gasdischarged after consumption from said oxygen-containing gas dischargepassage for humidifying the oxygen-containing gas supplied to saidoxygen-containing gas supply passage.
 7. A fuel cell system according toclaim 1, wherein said first and second fuel cell stacks are juxtaposedalong said stacking direction such that polarity of the first fuel cellstack and polarity of the second fuel cell stack are orientedoppositely.
 8. A fuel cell system comprising a fuel cell stack, whereinsaid fuel cell stack is formed by stacking a plurality of unit cells ina horizontal direction; each of said unit cells includes an electrolyteelectrode assembly and separators sandwiching said electrolyte electrodeassembly, and said electrolyte electrode assembly comprises a pair ofelectrodes and an electrolyte interposed between said electrodes; threeof six fluid passages comprising a fuel gas supply passage, anoxygen-containing gas supply passage, a coolant supply passage, a fuelgas discharge passage, an oxygen-containing gas discharge passage, and acoolant discharge passage extend through a left end of said fuel cellstack, and the other three of the six fluid passages extend through aright end of said fuel cell stack; a single first manifold is connectedto said three fluid passages provided at said left end of said fuel cellstack; a single second manifold is connected to said three fluidpassages provided at said right end of said fuel cell stack; and saidfirst and second manifolds are connected by a plurality of pipes.
 9. Afuel cell system according to claim 8, wherein said plurality of pipesare in contact with an end plate.
 10. A fuel cell system according toclaim 8, wherein adjacent pipes of said plurality of pipes are incontact with each other.